1. Field of the Invention
The present invention relates to a coaxial type starter device for an automobile engine.
2. Discussion of Background
A conventional coaxial type starter device is so constructed as shown in FIG. 6. Namely, the starter device comprises a direct current (dc) motor 1 having an armature rotary shaft 1a in a tubular form, a driving force transmitting means 3 provided at an end in the axial direction of the dc motor 1 and including a planet gear speed reducing unit 2, an output rotary shaft 4 supported in the armature rotary shaft so that the torque of the armature rotary shaft 1a is transmitted to it through a driving force transmitting means 3 and it is slidable in its axial direction, a pinion 5 provided at an end or the front end of the output rotary shaft 4 and an electromagnetic switch 6 provided at the other end in the axial direction of the dc motor 1 so as to feed a current to the dc motor and to move the output rotary shaft by pushing the plunger rod 6a, wherein the armature rotary shaft 1a of the dc motor 1 is arranged in alignment with the plunger rod 6a of the electromagnetic switch 6.
In such conventional coaxial type starter device, the electromagnetic switch 6, the dc motor 1 and the front machine frame 7 which receives the driving force transmitting means 3 are assembled together by means of two through bolts 8. Namely, each of the through bolts 8 is inserted into an opening formed in a flange portion 6c formed at the outer periphery of the front end portion of the casing 6b of the electromagnetic switch 6, so as to extend along the outer circumferential surface of the yoke 1b of the dc motor 1 and to be engaged with a screw portion formed in the front machine frame 7, whereby the casing 6b of the electromagnetic switch 6 and the front machine frame 7 are respectively brought in close contact with both ends of the yoke 1b of the dc motor 1; thus these three machine elements are combined together to form the coaxial type starter.
In the conventional starter device having the above-mentioned construction, since the through bolts 8 for connecting the electromagnetic switch 6, the dc motor 1 and the front machine frame 7 together are located outside the dc motor body, the through bolts 8 become obstacles when the coaxial type starter device 1 is attached to the engine. Accordingly, the conventional coaxial type starter device is difficult to attach to the engine.
In order to eliminate the above-mentioned problem, there is such a proposal that through bolts 35 are inserted from the rear end surface of the casing 25 of an electromagnetic switch 24 so that the bolts 35 extend inside a dc motor 1 as shown in FIGS. 7 and 8 (which is a cross-sectional view taken along a line VIII--VIII in FIG. 7). In this case, however, the size of an exciting coil 28c for the electromagnetic switch 24 is restricted because the through bolts 35 occupy a substantial area in the dc motor 1. Accordingly, the amount of lead wire wound in the exciting coil 28c is also limited.